Electronically commutated permanent magnet synchronous motors employ a complex control circuit to switch the energization of the various field windings at the proper time to keep the field and rotor in synchronism. In one approach, as the rotor and field rotate there are always two field windings energized and one unenergized at each segment of rotation and the windings which are energized and unenergized change with each segment. The switching of the windings at the fight time between the energized and unenergized states is done by integrating the back EMF of the unenergized winding until a threshold is reached at which point the switching is triggered. One shortcoming of this approach is that extremely high precision and expensive analog to digital conversion circuitry is required to insure that the back EMF derived switching is accurate. Another shortcoming is that the energizing voltage is generally constant, not sinusoidal, during a switching cycle so that the motors must be specially designed to be compatible with the control circuit.